SEPA transfers potentially reversible? How did you get that idea?
I have never heard of a single SEPA transfer being reversed, and I do read a lot about financial transactions in Europe, are on many groups and forums, and I would have heard about it if it was the case.
There are no more reversible then mailing a bunch of cash in an envelope to someone by mail.
AFAIK to "reverse" a SEPA you have to sue the recipient claiming you made a mistake, get a court order, and then a debt collector to get the money from the recipients account. That's the closest to "reversing" a SEPA as you can get.
Maybe you heard about SEPA direct debit being reversible, and made wrong conclusions? Direct debit is reversible, but that's a transfer initiated by the receiver - so like MtGox pulling money from your account. A sender-initiated SEPA transfer is not reversible (without suing).
If there is some kind of fraud involved it can be reversed. Same with wire transfers the banks will seek to claw the money back and your bank will just debit -1,000 or whatever out of your account.
It's very hard to get a bank account in Europe where you can receive a lot of incoming/outgoing SEPA. Banks will drop you quickly as it costs them extra money and they don't like doing it. Maybe there's some sort of SEPA payment gateway Gox could use instead of direct payments